Magnetic resonance image intensity ratio, a normalized measure to enable interpatient comparability of left atrial fibrosis

Heart Rhythm. 2014 Jan;11(1):85-92. doi: 10.1016/j.hrthm.2013.10.007. Epub 2013 Oct 3.

Abstract

Background: The measurement of late gadolinium-enhanced magnetic resonance imaging (LGE-MRI) intensity in arbitrary units limits the objectivity of thresholds for focal scar detection and interpatient comparisons of scar burden.

Objective: To develop and validate a normalized measure, the image intensity ratio (IIR), for the assessment of left atrial (LA) scar on LGE-MRI.

Methods: Electrocardiogram- and respiratory-gated 1.5 Tesla LGE-MRI was performed in 75 patients (75% men; 62 ± 8 years) before atrial fibrillation ablation. The local IIR was defined as LA myocardial signal intensity for each of the 20 sectors on contiguous axial image planes divided by the mean LA blood pool image intensity. Intracardiac point-by-point sampled electroanatomic map points were coregistered with the corresponding image sectors.

Results: The average bipolar voltage for all 8153 electroanatomic map points was 0.9 ± 1.1 mV. In a mixed effects model accounting for within patient clustering, and adjusting for age, LA volume, mass, body mass index, sex, CHA2DS2-VASc score, atrial fibrillation type, history of previous ablations, and contrast delay time, each unit increase in local IIR was associated with 91.3% decrease in bipolar LA voltage (P < .001). Local IIR thresholds of >0.97 and >1.61 corresponded to bipolar voltage <0.5 and <0.1 mV, respectively.

Conclusions: Normalization of LGE-MRI intensity by the mean blood pool intensity results in a metric that is closely associated with intracardiac voltage as a surrogate of atrial fibrosis.

Keywords: AF; Atrial fibrillation; EAM; Electroanatomic mapping; IIR; LA; LGE; Late gadolinium–enhanced magnetic resonance imaging; MRI; PV; Scar; atrial fibrillation; electroanatomic map; image intensity ratio; late gadolinium enhancement; left atrial; magnetic resonance imaging; pulmonary vein.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Atrial Fibrillation / diagnosis
  • Atrial Fibrillation / etiology*
  • Atrial Fibrillation / physiopathology
  • Body Surface Potential Mapping
  • Cardiomyopathies / complications
  • Cardiomyopathies / diagnosis*
  • Diagnosis, Differential
  • Electrocardiography
  • Female
  • Fibrosis / pathology
  • Follow-Up Studies
  • Heart Atria / pathology*
  • Humans
  • Image Processing, Computer-Assisted / methods*
  • Magnetic Resonance Imaging, Cine / methods*
  • Male
  • Middle Aged
  • Myocardium / pathology*
  • Reproducibility of Results
  • Retrospective Studies